This invention relates to an improved process for preparing fiberboard having water resistance and improved releasability and to the treated fiberboard thus produced.
Fiberboards (sometimes called pressed boards or hardboards) are boards manufactured from cellulosic fibers interfelted, preferably with a binder material, to produce an initial adhesive bond among the fibers. In a typical preparation procedure, the wet interfelted panels are shaped and cut to the approximate desired dimensions, (ordinarily to form a semi-hard board) and transferred to a drying and baking oven wherein the remaining moisture is evaporated and the boards are baked to set the binders therein. To allow the fiber panel to be released from the platens in the press for subsequent compression to size, the panel is typically treated, prior to drying and compression, with a hydrocarbon resin. An additional treatment of the basic board for water resistance (tempering) is often carried out with various combinations of polymeric materials and drying oils. Thus, the compressed, hot board may be immersed in a bath of a siccative material such as a drying oil or drying oil blend of oxidized resins so that the surface and edges of the board are impregnated with up to 6% of the oil. The treating oil may also be applied by spraying or roll coating. The impregnated board is then baked at high temperature to oxidize (polymerize) the drying oil to a tough, insoluble form, to yield the tempered fiberboard in final form. The fiberboard exhibits greatly improved physical properties such as resistance to moisture, strength, hardness; possesses paintability and machinability, and is mostly used in applications in which it is likely to be exposed to external conditions of weather or dampness.
There is therefore a need for a one-step process for preparing fiberboard wherein the separate applications of hydrocarbon resins for release properties and of drying oil for water resistance are replaced by a one-step application of an aqueous composition which will provide a fiberboard having water resistance and releasability equal to or better than the tempered fiberboard of the prior art.